Re: Weird PUFFS reclaim activity on netbsd-6

On Thu, Mar 08, 2012 at 05:32:47AM +0100, Emmanuel Dreyfus wrote:
> A posible explanation: perfuse tries to reuse nodes. If the same node is
> looked up twice and not reclaimed in between, perfuse return the same
> node
Further experiments suggest this is the problem. netbsd-6 can lookup
multiple time the same node without sending a reclaim. But at the end,
there will be as many reclaims as lookups. If perfuse tracks the
lookup/reclaim counts and ignore reclaims until it gets to zero, things
seems to work fine.
But this new behavior does not seems very smart on the performance front.
The kernel sends a lookup for a nodes it already knows, and it sends
reclaims that must be ignored. In the context of PUFFS filesystem,
unnecessary VFS ops has a real cost. Is there some rationale behind
this change?
--
Emmanuel Dreyfus
manu%netbsd.org@localhost